Vulcanizing rubber



Patented Sept. 5, 1933 PATENT OFFICE VULCANIZING RUBBER George H.Stevens, Newark, N. J.

No Drawing. Application February 29, 1928 Serial No. 258,148

10 Claims.

, This invention relatesto improvements in the use of organicnitrogenous substances that assist in or accelerate the vulcanization ofrubber, and has for its object the utilization of new chemical reactionsand products to this end.

This specification is a continuation in part of Ser. No. 651,968 filedJuly 16, 1923, relating to the use of mono and tri-substitutedguanidines in combination. V

Tri-phenyl guanidine (CmI-InNs), has been known for along time as anaccelerator, but the results obtained from the use of it are not equalto that of many other accelerators that are just as available foruse,and while it has over 14% F of nitrogen it still fails to rate with thebest of combine them, and find properties present then more conducive toeffecting an accelerated vulcanization than is found in either when usedalone.

Mono-phenyl guanidine has a melting point of 66 C., and a nitrogencontent of 31%, while the melting point of tri-phe'nyl guanidine is 1430., and the nitrogen content 14.6%. The formeris quite hydroscopic andsoluble in water. The latter is practically non-hygroscopic and onlyslightly soluble in water.

Mono-phenyl guanidine decomposes readily at a temperature a littleaboveits melting point and in so doing splits ofi? ammonia, withcarbomonophenylimide (or its equivalent phenyl cyanamide,

or cyanilide, (CvHeNz) as the main decomposition product, of very lowmelting point and readily polymerizable to a much higher melting point.Its tri-molecular polymerization product being a melamine withthreephenyl groups or substitutions.

Tri-phenyl guanidine, while it does not decompose at as low atemperature as the mono-phenyl guanidine, nevertheless decomposesreadily at vulcanizing temperatures and splits olf aniline, with itsmain decomposition product as carbodiphenylimide (or its equivalentdiphenylcyana mide Clal-lmNz), also of very low melting point andreadily polymerizable to a much higher melt- Decomposition of themono-phenyl guanidine ing point. Its tri-molecular polymerization prod-I not being a melamine with six phenyl groups or substitutions.

Carbomonophenylimide and carbodiphenylimide are both of them veryreactive bodies and especially so in the presence of any aminedecomposition products that may be present with them.

They will polymerize with each other in more than one molecularproportion, each will combine with either aniline or ammonia, and eitherwill combine with more than one phenyl substituted guanidine.

The carbomonophenylimide and carbodiphenylimide polymerization productsare alsomore or less reactive with the same bodies as their lowerpolymers.

The aniline and ammonia released with these two phenyl substitutedcarbodiimides is also reactive with more than one of the phenylguanidines.

In the .reactions then that follow, from a combination of mono-phenylguanidine and tri-phenyl guanidine under vulcanization, and with ametallic oxide present, the result would appear to be largely asfollows:-

into carbomono-phenylimide and ammonia.

Decomposition of the tri-phenyl guanidine into carbodiphenylimide andaniline.

- Combination of carbodiphenylimide with the nascent ammonia todi-phenyl guanidine, and probably combination of some of thecarbomonophenylimide and nascent aniline also to di-phenyl guanidine.

Nascent di-phenyl guanidine (supposedly far more. active than normaldi-phenyl guanidine), might largely be the first product formed, thoughsubstantially only as an intermediate product, but subjectto the samegeneral trend of decomposition as any di-phenyl guanidine.

, This normal decomposition of di-phenyl. guanidine is authoritativelyagreed upon as: First splitting up into carbomonophenylimide andaniline,

tuted guanidines, unchanged phenyl substituted carbodiimides, and thephenyl substituted carbodiimide combination products that possessmelting points above that of the products started with, and ofconsiderable stability.

In vulcanization then, this would indicate an early activity of theaccelerator composed oi? mono-phenyl guanidine and tri-phenyl guanidinewhile the disassociation reactions were taking place and aniline andammonia were being split off, than a reaction stage where the phenylsubstituted carbodiimides were forming new products with the othercomponents, and then an ultimate stage where the progressive reactionswere accumulating higher melting bodies in place of the lower meltingbodies started with.

These stages of reaction however are not to be understood as distinctlyseparate but are periods Where the stated reactions may predominate.

Conflicting opinions exist as to what these ultimate bodies really are,for varying temperatures of vulcanization and different vapor pressuresto which a vulcanization may be subjected, may somewhat change the orderof decomposition of the inonoand t'ri-iphenyl guanidines, and also"change the speed of dissipation of the aniline or ammonia, or evenchange the order of recombination of the disassociation products, butall of these reactions take place substantially between but fourimportant constituents, namely: carbomonophenylirnide,carbodiphen'ylimide, aniline and ammonia. 1

It is plainly evident then that largely the same end maybe attained inany of these reactions, and that variations in temperature and pressuremust influence more the degree of such ultimate conversion than it wouldthe production of any compounds other than would normally occur betweenthese four products, and that ultimately tetra-phenyl melamine(tetra-phenyl tricarbodiimide) (C27H22N6 M. P. 217 C.) may constitute asubstantial part if the reaction is carried far enough.

Varying the percents of the two phenyl guanidines employed, will ofcourse cause a variation in "the quantity of the respective phenylsubstitutedcarbodiimides liberated, as well as vary the quantity ofaniline and ammonia split on, which in turn probably governs toa'considerable extent the production of the higher melting resultantbodies that would be formed. 1

The foregoing relates to the'two phenyl substitutedguanidines mentionedand to their decomposition products. 1

However, much the same series "of reactions seem to also take placebetween the two tolyl, and between the two xylil correspondinglysubstitu'ted guanidines, as well as between any monoand tri-arylsubstituted guanidines that'are homologous to them, the radicals orsubstituting 'groupsof which are derived from primary phenyl amines"and'that necessarily will. have more than .six carbon atoms.

While aniline enters into the production of the I phenyl substitutedguanidines mentioned,-'and is also a decomposition product of them aswell, in a like manner toluidine, Xylidine, or themona m ines homologousto aniline, bear a similar rela- Aniline and these homologues ofaniline, in their chemical activity however, are not necessarilyconfined to reactions within their own group,

for if they be present in a different group they may also causereactions that result in compounds containing both of such homologousradicals or groups, as where combination is made between amono-substituted guanidine and a trisubstituted guanidine, each of whichmight contain a different homologous radical or group.

Such combinations might be especially desirable, so that a low meltingmono-substituted guanidine could bring down the melting point of a highmelting tri-substituted guanidine, or vice versa as a solid solution,and thus allow both to accelerate vulcanization at their maximumefficiency.

In my investigation of that series of compounds, of which the severalexamples have been mentioned, I have found that such a solid solution ofmono-substituted guanidines and tri-sub- 'stituted guanidines, where thesubstituting groups are of the phenyl, tolyl, xylil, or homologous arylgroups that may be derived from primary phenyl amines, do prove ofunusual value in accelerating rubber vulcanization.

Mono-phenyl guanidine is readily made by 'desulphurizing mono-phenylthiourea in the presence of ammonia (Feuerlein, Ber. 1879, 12 '1602).

mustard oils (ary l substituted iso-thiocyana-tes) and ammonia.

Mono-phenyl guanidine is also made by combin-ing mono-phenylsubstituted'carbodiimide and ammonia (Beilstein, 1883, II, 920). If themonosubsti'tuted ca-rbo'diim-ide has a tolyl, xylil; or homologous 'arylradical or substituting group in place of the phenyl group,a-corresponding monotolyl, "mono xylil, or homologous mono-arylsubstituted guanidine results, and with an alkyl substitution in thearyl group.

'The'benzene ring-oi the radical or substituting group in any arylsubstituted guanidine, other than phenyl substituted guanidine, andhomologous thereto,-must contain at least one alkyl sub- 's'titutinggroup, and any such aryl substituted guanidine having an alkylsubstitution, exists "then in several different isomeric forms, theisomeric form depending upon the position that the alkyl group takes inits substitutionof hydrogen of the benzene ring,

Another method of producing mono-phenyl guanidin'e'is from cyanamide(carbodiimide) and "aniline hydrochloride (McKee, Am. Chem. JnL,

1901, 26, 221; Kaempf, Ber. 1904, 37,1681; Rich- .ter, 1922, II, 104),the acid salt of course being neutralized to obtain the base.

lvlono-phenyl guanidine is also a decomposi- 'tion-product-o'fphenyl-biguanide (Monatsh. 1891,

The most-convenient Way to make tri-phenyl guanidineis to desulphurizedi-phenyl' thiourea (th-iocar'banilide), with litharge inthe presenceof-aniline. This process is one in quite general "commercial use.

A desulphurization of monoand di-plienyl thiourea (without aniline),also gives the same phenyl substituted 'carbodiimides, as does the,decomposition or" the corresponding monoand triphenyl guanidines.

r'flono-to'lyl guanidine, mono-xylil guanidine, or

any'monmaryl substituted guanidine homologous to'mono-phenyl guanidine,may in a like manner tioned processes, and the tri-aryl substitutedisomeric forms, has a melting point about 20 below that of tri-phenylguanidine.

These melting points vary slightly as the percents of the constituentisomers vary.

A combination then of these two phenyl guanidines into a solid solution,may be readily effected and in several difierent ways.

One manner of preparing the solid solution phenyl guanidine acceleratoris to use molecular proportions, and take twice the molecular proportionof the lower melting or Y mono-phenyl guanidine, and one molecularproportion of the higher-melting or tri-phenyl guanidine.

Reduced to specific quantities the proportions would be, about 15 ozs.of mono-phenyl guanidine and 16 ozs. of tri-phenyl guanidine.

The nitrogen content of the mixture then would be. a little above 25%which would be rated very high ina suitable accelerator.

Should molecular proportions of the monoand tri-phenyl guanidine beused, theoretically no aniline or ammonia would be left over, andtheoretically an equal weight of nascent diphenyl guanidine would resultas one of the first combination products of the disassociation. Thenitrogen content would then be over 19%.

As a large quantity of the low melting monophenyl guanidine (M. P. 66C.), might lower the melting point of the combined product to such anextent as to possibly interfere with its usefulness, a less amount of itmight be preferable.

To combine these two substituted guanidines into a solid solution, theymay be melted together by heat, or be precipitated together from a saltsolution of both, or they may be recovered from a mutualsolvent of both,whereupon the resultant solid solution will then have a single or commonmelting point.

While the above proportions may seem to be the most desirable, yet theproportions may be changed considerably to meet various vulcanizingconditions. I

These combinations of mono-phenyl guanidine and tri-phenyl guanidine, ormixtures of their equivalents as accelerators, appear then to derivemuch of their effectiveness from thepeculiar circumstance that thedisassociation inter-reactions between the two phenyl substitutedguanidines cause the gradual formation, within the.

heated rubber, of nascent di-phenyl guanidine a an intermediate. I

This intermediate di-phenyl guanidine forms then while thedisassociation products are also forming, and the intermediate ornascent diphenyl guanidine, or any similarly formed disubstitutedguanidine homologous to di-phenyl guanidine, is capable of greatactivity, as it breaks up however, it follows then the usualdisassociation course.

Combinations of the monoand tri-substituted guanidines homologous tothese phenyl substituted guanidines, show substantially the samereaction behavior under the same vulcanizing temperatures, and in usingthem they would be combined in the same way as the phenyl substitutedguanidines.

The following representative formula shows the use of tolylsubstitutedguanidines in place of phenyl substituted guanidines, in a vulcanizablerubber mixture.

82 lbs. smoked sheets 5 lbs. zinc oxide 7 lbs. barytes 5 /2 lbs. sulphur,2 oz.monotolyl guanidine Combined into a 5 oz.'tri-tolyl guanidinesolid solution ccf lbs. total Vulcanized at 40 lbs. steam pressure infrom 25 I to 35 minutes.

My invention then consists in making use of these monoandtri-substituted guanidines in a new manner, that initiates quite new anddifferent reactions during vulcanization, and that greatly acceleratesthe vulcanization of the rubber in which they are employed, givingresultant vulcanized products that are highly improved.

It is to be understood that I do not mean to limitmyself to theingredients, components, or proportions given in this specification, orto merely such examples as have been cited by me, it being readilyunderstood by those well versed in the art, that the said ingredients,components, and proportions may be varied within comparatively widelimits without departing from the principles and purposes of myinvention as herein set forth.

Having now described my invention and having shown in what manner thesame may be utilized, what I claim as new, and desire to secure byLetters Patent is:

1. A process of vulcanizing rubber which consists in, incorporating intocompounded rubber an accelerator comprising a combination of monotolylguanidine with symmetrical tri-tolyl guanidine as a solid solution, thenheating the resultant rubber mixture with a vulcanizing agent to effectvulcanization.

2. A process of vulcanizing rubber which comprises, incorporating avulcanizing agent with compounded rubber, then applying heat andeffecting an accelerated vulcanization in the presence of a solidsolution of a mono-tolyl guanidine and a symmetrical tri-tolyl guanidinein the ruber mixture.

i 3. A process of vulcanizing rubber which consists in, incorporatinginto rubber an accelerator comprising the combination of a solidsolution of two or more isomeric mono-tolyl guanidines and two or moreisomeric symmetrical tri-tolyl guanidines, then heating the resultantrubber mixture with a vulcanizing agent to effect vulcanization. Y

4. A process of vulcanizing rubber which consists in, incorporating intocompounded rubber an accelerator comprising a combination ofmonosubstituted guanidine with tri-substituted guanidine, as a solidsolution, both guanidines being substituted by aromatic groups derivedfrom primary phenyl amines, and each of the aromatic groups having morethan six carbon atoms, then heating the resultant rubber mixture with avulcanizing agent to effect vulcanization.

5. A process of vulcanizing rubber which comprises, incorporating avulcanizing agent with compounded rubber, then applying heat andeffecting an accelerated vulcanization in the presence of a solidsolution of a mono-substituted guanidine and a symmetricaltri-substituted guanidine in the rubber mixture, one of the guanidinesbeing substituted by the tolyl group,

the other guanidine being substituted by a group that is homologous tothe tolyl group, and derived from a primary phenyl amine, but containingmore than six carbon atoms, and the homologous group derived from aprimary phenyl amine.

6. A process for accelerating the vulcanization of rubber whichcomprises combining the rubber with a vulcanizing agent, and a solidsolution of mono-substituted guanidine and symmetrical trisubstitutedguanidine, the substituted guanidines having hydrocarbon substitutingaryl groups derived from primary phenyl amines, and each of the arylgroups having an alkyl substitution for at least one of its hydrogens,and vulcanizing the rubber. 1 v I 7. A process .for accelerating thevulcanization of) rubber which comprises combining the rubber with avulcanizing agent, and a combination of the solid solution of two ormore isomeric monoaryl substituted guanidines and two or more isomericsymmetrical tri-aryl substituted guanidines, and the aryl groups .ofboth guanidines :being derived from primary phenyl amines, andvulcanizing the rubber.

:8. A vulcanized compound derived from compounded rubber or similarmaterial combined with a vulcanizing agent and a solid solution ofmonotol'yl ,guanidine and symmetrical tri-tolyl guanidine.

9. A process of vulcanizing rubber which consists in, modifying themelting point of symmetrical tri-substituted guanidine, by incorporatingmono-substituted guanidine with it into a solid solution as a modifiedsubstituted guanidine accelerator, the substituting groups of bothguanidines to be arylgroups containing more than 6 carbon atoms and thearyl groups derived from primary phenyl amines, then incorporating theaccelerator thus formed. into compounded rubber, and then heating theresultant rubber mixture with a vulcanizing agent to effectvucanization.

10. A vulcanized compound derived from compounded rubber or similarmaterial combined with a vulcan-izing agent and a solid solution ofmonosubstituted guanidine and symmetrical tri-substituted guanidine, oneof the guanidines-being substituted by the tolyl group, the otherguanidine being substituted-by a group that is homologous to the tolylgroup but containing more than 6 carbon atoms, and the homologous groupderived from a primary phenyl amine.

GEORGE H. STEVENS-.-

